Battery monitoring system with integrated battery holder

ABSTRACT

An apparatus for monitoring the condition of a battery. The apparatus includes a battery clip that is used to secure a battery to a battery connection and a battery monitoring IC. The battery monitoring IC takes a “load vs. no-load measurement” and the results are recorded in a register. When the battery reaches a certain low voltage state, register bits are set and an output is generated. Furthermore, the exemplary embodiment includes a removal detection circuit for detecting removal and replacement of the battery and for preventing voltage floating on the battery output line.

This application is a division of application Ser. No. 09/359,940, filedJul. 22, 1999 now U.S. Pat. NO. 6,208,114.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to battery monitoring circuitry and moreparticularly, but not by way of limitation, to a battery monitoringsystem that includes an integrated battery holder.

2. Background of the Problem and Related Art

It is well known that a primary battery is a convenient source of powerfor portable electric and electronic devices. Small size, ease of use,low maintenance and good shelf life are just a few of the reasons thatprimary batteries are frequently used in modern electronics. Forexample, primary batteries are regularly used in PCS and servers to keepa time of day clock running even when the particular device is nototherwise powered.

Because the primary battery is such a convenient and reliable source ofpower, many electronic devices also use the primary battery as a sourceof backup power, such as for CMOS memory—thereby preserving the contentsof the memory even when the memory is not otherwise powered. In fact,the computer and electronic industry has incorporated the coin-shapedprimary battery into the majority of devices that require a backup powersource.

Because the primary battery often protects critical data from corruptionand loss, a user cannot allow the battery to fail. The failure of aprimary battery could mean disastrous data corruption, data loss and/orsystem downtime—all of which are unacceptable in today's informationcritical systems. Accordingly, it is vital that a user or systemadministrator be able to easily and accurately determine when a primarybattery is nearing failure (but not yet completely depleted) and shouldbe replaced.

Furthermore, it is vital that a primary battery be replaceable withoutcorrupting the data it is backing up. In existing devices, replacing aprimary cell allows voltage at the backed-up device to float. Forexample, FIG. 1 illustrates a block diagram of a battery backed, device105 connected to a primary battery 110 through a supply voltage line 115and a battery output line 120. The primary battery 110 is also groundedat ground 125. In this device, when the primary battery 110 is removedor inserted, the voltage on line battery output 120 momentarily changes,i.e., floats, and likely creates a condition in the battery backeddevice 105 that results in data corruption or other damage.

In light of the above-described and other deficiencies in the existingart, a device is needed that accurately monitors the characteristics ofa battery, particularly the characteristics of a primary battery used inelectronic systems. Furthermore, a device is needed that prevents thevoltage on the primary battery's output line from floating when thebattery is replaced.

SUMMARY OF THE INVENTION

To remedy the deficiencies of existing systems and methods, the presentinvention provides, among other things, an apparatus to accuratelymonitor the characteristics of a battery. Furthermore, the presentdevice prevents the voltage on the primary battery's output line fromfloating when the battery is replaced.

In an exemplary embodiment, but by no means the only embodiment, theinvention includes a battery clip that is used to secure a battery to abattery connection and a battery monitoring integrated circuit (IC). Thebattery monitoring IC takes a “load vs. no-load measurement” and theresults are recorded in a register. When the battery reaches a certainlow voltage state, register bits are set and a low battery signal isgenerated. Furthermore, the exemplary embodiment includes a removaldetection circuit both for detecting removal and replacement of thebattery and for preventing voltage float on the battery output line.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and more complete understanding of thepresent invention will become apparent and more readily appreciated byreference to the following Detailed Description and to the appendedclaims when taken in conjunction with the accompanying Drawings wherein:

FIG. 1 is a block diagram of a battery backed device connected to aprimary battery;

FIG. 2 is an exploded perspective of a battery holder including abattery monitoring integrated circuit (IC);

FIG. 3 is a block diagram of the electronics of the battery holder shownin FIG. 1;

FIG. 4 is a “voltage vs. time” plot for a no-load voltage measurementand a loaded voltage measurement; and

FIG. 5 is a more detailed block diagram of the battery monitoring ICshown in FIGS. 2 and 3.

DETAILED DESCRIPTION

Although the present invention is open to various modifications andalternative constructions, a preferred exemplary embodiment that isshown in the drawings is described herein in detail. It is to beunderstood, however, that there is no intention to limit the inventionto the particular forms disclosed. One skilled in the art can recognizethat there are numerous modifications, equivalences and alternativeconstructions that fall within the spirit and scope of the invention asexpressed in the claims.

Referring now to FIG. 2, there is illustrated an exploded perspective ofa battery holder 200 with a battery monitoring integrated circuit (IC)225, which can be a microcontroller. In particular, there is illustrateda battery clip 205 that is attachable to a printed circuit board (PCB)210. By attaching the battery clip 205 to the PCB 210, the battery 215can be secured such that the cathode of the battery 215 is in contactwith a metallic contact 220, such as a gold plated contact, located onthe PCB 210. Additionally, pins 230 are also connected to the PCB 210.

In one embodiment, the battery clip 205 is constructed with nickelplated spring steel. In this embodiment, the battery clip 205 can beeasily removed and attached to the PCB 210. Accordingly, the battery 215can be easily replaced. Furthermore, the size of the battery clip 205and the PCB 210 can be varied according to the diameter and thickness ofany battery or type of battery—thereby minimizing the possibility ofattaching the wrong type, size or diameter battery.

The PCB 210 and the battery clip 205 can form a discrete component thatis not manufactured as a portion of a main system board, e.g., amotherboard. That is the PCB 210 and the battery clip 205 can bemanufactured and sold separately from any system board. As can beappreciated, the discrete component including the PCB 210 and thebattery clip 205 can be attached to a system board at any time.

Referring now to FIG. 3, there is illustrated a block diagram of theelectronics of the battery holder 200 shown in FIG. 2. The batterymonitoring IC 225, as shown in FIG. 3, is connected to five lines: asupply voltage line 235, a serial data line 240, a serial clock line245, a battery output line 250, and a ground 255. These lines aregenerally connected to separate ones of pins 230 (shown in FIG. 2). Theserial data line 240 and the serial clock line 245 form a 2-wireinterface used to communicate with the battery monitoring IC 225.Furthermore, for control purposes, both the serial data line 240 and theserial clock line 245 are connected to the supply voltage line 235 byindividual resistors 260 and 265.

In operation, the battery monitoring IC 225 operates by comparing theexisting battery's condition against known battery characteristics. Thisis done while supply voltage is being applied to the battery monitoringIC 225 and while the battery is not loaded by the system. Moreparticularly, the battery monitoring IC 225 performs a pair of voltagemeasurements on the battery output line 250. The first measurement is avoltage measurement taken when there is no load. The second measurementis also a voltage measurement. However, the second measurement is takenwhen there is a load. The difference between these two measurements isDELTA-V. The measurement DELTA-V, when taken over time, can be used togauge the remaining useful capacity of the battery 215. Alternatively, asingle DELTA-V measurement can indicate that the battery is nearing theend of its useful life.

FIG. 4 illustrates a typical “voltage vs. time” plot for a no-loadvoltage measurement and a loaded voltage measurement. Measurement plot270 represents an exemplary plot of the voltage for the no-loadmeasurement and measurement plot 275 represents an example of thevoltage plot for the loaded measurement. The difference between thesetwo measurement plots at a particular time is represented by DELTA-V280.

As illustrated by FIG. 4, the typical battery and its voltage outputcapacity continually degrade. By monitoring DELTA-V 280, a low batterycan be identified before the battery is completely drained. As can beappreciated, the voltage from the no-load measurement 270 remains fairlyconstant until the battery is virtually depleted (time t2). The voltagefrom the loaded measurement 275, on the other hand, begins to fallrapidly near the end of the battery's life (after time t1) but wellbefore the battery is depleted (time t2). Accordingly, DELTA-V growssubstantially near the end of the battery's life (after time t1). Thebattery monitoring IC 225 can detect this growth in DELTA-V or detectwhen DELTA-V exceeds a certain threshold and notify a user that thebattery 215 is nearing failure and should be replaced. Alternatively,battery monitoring IC 225 can provide the DELTA-V information to othercircuitry that can notify the user of the battery's condition.

FIG. 4 represents only an exemplary plot of the “load vs. no-load”characteristics of a primary battery. Each type of battery, e.g., CR(lithium/manganese dioxide) and BR (lithium/carbon monofluoride), hasits own characteristics that can be programmed into the batterymonitoring IC 225. Thus, the battery monitoring IC 225 can be adapted todetect a low battery condition for any battery chemistry. Furthermore,the battery monitoring IC 225 can be programmed to detect a low batterycondition for any particular battery capacity or other batterycharacteristic.

Referring now to FIG. 5, there is illustrated a more detailed blockdiagram of the battery monitoring IC 225 shown in FIGS. 2 and 3. In thisembodiment, the battery monitoring IC 225 includes a logic element 285connected to both a serial interface 290 and a register bank 295, whichincludes a battery low output 315. The battery monitoring IC 225 alsoincludes a battery removal detector 300 and a measure control logic 305,both of which are connected to the register bank 295. Furthermore, themeasure control logic 305, which provides various logical capabilities,is connected to an analog-to-digital (A/D) converter 310.

Continuing to refer to FIG. 5, a DELTA-V measurement cycle is initiatedwhenever the supply voltage 235 is cycled or upon command from the hostsystem (not shown) through the use of the register bank 295. As can beappreciated, for systems that are rarely powered down, the host systemhas the primary responsibility for initiating the DELTA-V measurement.

When a DELTA-V measurement cycle is initiated, the battery monitoring IC225 measures the no-load battery voltage. Next, the battery monitoringIC 225 attaches a load to the battery for a select amount of time andtakes a voltage measurement during that time. Although the size of theload and the length of time that the load is attached to the battery canvary, particularly good results have been obtained by attaching a 1.2MΩload for one second. Because voltage measurements are generally analog,both measurements are converted to a digital format using the A/Dconverter 310. In one embodiment, the voltage measurement is an 8-bitsuccessive approximation of the analog voltage measurement. One skilledin the art, however, can understand that other voltage measurementand/or data conversion schemes can be used to achieve similar results.

After both measurements have been taken and converted, the DELTA-V valueis determined and stored in the register bank 295. This DELTA-V value isavailable over the 2-wire bus (lines 240 and 245 connected to the serialinterface 290) to a host system (not shown) for particular batterymonitoring options. Although particularly good results have beenobtained by using the 2-wire bus, it is contemplated that otherinterfaces can be used instead of the 2-wire bus.

Next, when the DELTA-V sensing circuit 285 senses that the battery 215is low, i.e., below a certain threshold, a battery status bit (notshown) in the register bank 295 is set to logic 0 and the battery lowoutput 315 is driven to active low. Once set, the battery status bitremains logic 0 and the battery low output 315 remains asserted untilthe battery 215 is physically replaced.

The logic element also controls two additional bits in the register bank295: a measurement status bit and a new measurement bit (neither ofwhich are illustrated). The measurement status bit is set when a DELTA-Vmeasurement cycle is in progress. The new measurement bit is set when aDELTA-V measurement cycle completes.

Continuing to refer to FIG. 5, the battery removal detector 300 candetect when the battery 215 (shown in FIGS. 2 and 3) is removed from orinserted into the battery holder 200 (also shown in FIGS. 2 and 3) and,responsive to detection of a battery 215 removal/insertion, set ano-battery bit in register bank 295. When the battery is replaced, theno-battery bit is flipped. Furthermore, when the battery is replaced,the new battery bit is set to logic 1. One advantage of the batteryremoval detector 300 is that it enables the battery 215 to be replacedwhile the system is “hot” or powered up.

Although the register bank 295 can be arranged in a variety of ways,particularly good results have been obtained when the register bank 295includes a status register, a control register and a DELTA-V register(none of which are illustrated). The status register included in theregister bank 295 provides information regarding the DELTA-V measurementprocess, the battery capacity state and battery replacement detection.Furthermore, the bits in the status register fall into two additionalcategories: those that are cleared after they are read and those are notaffected by being read. For example, the new measurement bit and the newbattery bit are cleared after they are read. The measurement status bit,the battery status bit and the no battery bit, on the other hand, arenot affected by being read.

In an exemplary embodiment, the control register (not shown) included inthe register bank 295 can be a write only register that is used toinitiate a DELTA-V measurement cycle. In operation, a host system canwrite a logic 1 to this register and cause the logic element 285 toperform a DELTA-V measurement. The control register is particularlyimportant for systems that are rarely powered down because the systemcan initiate a DELTA-V measurement cycle instead of waiting for thesystem to be powered down and back up.

The DELTA-V measurement register (not shown) included in the registerbank 295 stores the results of the most recent DELTA-V measurementcycles. In one embodiment, the DELTA-V measurement register is a readonly register that stores the last eight DELTA-V measurements. Thesestored DELTA-V measurements are accessible to the host system throughthe 2-wire bus (serial data line 240, serial clock line 245 and serialinterface 290).

In conclusion, one skilled in the art can appreciate that the presentinvention provides an apparatus for monitoring the condition of abattery. In the exemplary embodiment, a battery clip is used to secure abattery to a battery connection and a battery monitoring IC. The batterymonitoring IC takes a “load vs. no-load measurement” while Vcc isapplied, and the results are recorded in a register. When the batteryreaches a certain low voltage state, register bits are set and an outputis generated. Furthermore, the exemplary embodiment includes a removaldetection circuit for detecting removal and replacement of the batteryand for preventing voltage float on the battery output line.

Those skilled in the art will readily recognize that numerous variationsand substitutions may be made in the invention, its use and itsconfiguration to achieve substantially the same results as achieved bythe embodiments described herein. For example, bit configurations, logicvalues and component groupings can be easily altered. Accordingly, thereis no intention to limit the invention to the disclosed exemplary forms.Many variations, modifications and alternative constructions will fallwithin the scope and spirit of the disclosed invention as expressed inthe claims.

What is claimed is:
 1. A battery monitoring circuit comprising: ameasurement circuit element for performing a DELTA-V measurement; astorage device for storing the DELTA-V measurement; and an interfaceconnected to the storage location, the DELTA-V measurement stored in thestorage device being accessible through the interface; and a signalcircuit element for signaling a low battery condition responsive to theDELTA-V measurement.
 2. The battery monitoring circuit of claim 1wherein an indicator of a low battery is stored in the storage device.3. The battery monitoring circuit of claim 1, wherein the batterymonitoring IC comprises: a battery removal detector for detectingremoval of the battery.
 4. The battery monitoring circuit of claim 3,wherein the battery removal detector limits voltage float on a batteryoutput line.
 5. The battery monitoring circuit of claim 1 furthercomprising: a primary cell coupled with the measurement circuit element.